The present invention relates to a driving device for a thread hooking mechanism for a sewing machine and, more particularly, to a driving device for a threading hooking mechanism for a sewing machine requiring a larger sewing space for a workpiece with a large thickness.
FIGS. 1-4 show a sewing machine suitable for stitching a fluffy, multilayer workpiece such as cloth or leather. The sewing machine includes a body 10 having upper and lower beams 11 and 12. A head 13 is mounted to an end of the upper beam 11. A needle plate base 20 is mounted to an end of the lower beam 12 and aligned with the head 13. A transmission shaft 15 extends in the upper beam 11 and can be driven by a power source 14 in the form of a motor via a pulley 14 and a belt 142. A transmission shaft 16 extends in the lower beam 12 and is connected to an end of the transmission shaft 15 by pulleys 151 and 161 and a timing belt 152. A stitching device 17 is coupled to the other end of the transmission shaft 15 and includes a needle 171 and a pressing device 18 having a pressing leg 181. When the motor 14 is activated, the needle 171 and the pressing legs 181 move reciprocatingly in a vertical direction. When sewing a workpiece having a larger thickness in the vertical direction, a thread hooking mechanism 19 is driven by the transmission shaft 16 via a driving device 50, so as to hook a thread on the stitch 171 and a bottom thread on a shuttle core 193 of a shuttle 192 in the thread hooking mechanism 19 for the purposes of sewing operation.
Specifically, a transmission wheel 51 is mounted on an end of the transmission shaft 16 and connected via a timing belt 54 to a driven wheel 53 mounted on a driven shaft 52 that is driven by the timing belt 54. The other end of the transmission shaft 16 extends into the needle plate base 20. The thread hooking mechanism 19 rotates at a speed two times of that of the transmission shaft 16. Furthermore, two tension wheels 55 and adjusting wheel seats 56 as well as adjusting bolts 57 and 58 are provided to adjust the tension of the timing belt 54.
The spacing between the head 13 and the needle plate base 20 is fixed, and the spacing between the transmission shaft 16 and the driven shaft 52 in the vertical direction provides a larger space between a bottom face of the upper beam 11 and a top face of the lower beam 12 for the purposes of easy sewing operation. However, the conventional driving device 50 has quite a few members and requires troublesome manufacturing, processing, assembling, and adjustment, leading to a waste in labor and time while increasing the costs. Furthermore, the timing belt 54 is liable to wear out and not easy to be detached for maintenance.
Thus, a need exists for a novel driving device for a threading hooking mechanism for a sewing machine that is simple in structure, more durable, easy to manufacture, easy to process, and easy to assemble, so that the manufacturing costs can be reduced and that the functionality can be enhanced.